This invention relates to printing machines, and more particularly this invention relates to a heat transfer station on an image support surface of a printing machine.
Electrostatographic printers are known in which a single color toner image is electrostatically formed on photoreceptive image bearing member. The toner image is transferred to a receiving substrate, typically paper or other print receiving materials. The toner image is subsequently fused to the substrate.
In one arrangement of an electrostatographic printer, a plurality of dry toner imaging systems each having an image bearing member, are used to develop multiple color toner images. Each color toner image is electrostatically transferred from the image bearing members and onto an intermediate transfer member to form a multilayer composite toner image. The composite toner image is electrostatically transferred to a transfuse member and finally transferred and fused to the final substrate. Such systems that use electrostatic transfer to transfer the composite toner image from the image bearing members to the intermediate transfer member, and from the intermediate transfer member to the transfuse member, can have transfer limitations. In operation, the transfuse member is cooled below the glass transition temperature of the toner prior to the transfer nip with the intermediate transfer member. Cooling of the transfuse member requires the transfuse member to be relatively thin. A thin transfuse member however has low conformance therefore providing reduced transfer efficiency in the transfuse nip. The reduced conformance also increases the potential for glossing of the toner image in the transfuse nip. In addition, a thin transfuse member can have a reduced operational life.
Briefly stated, a heat transfer station in accordance with the invention transfers heat from the post-transfer region of a toner image bearing member to the pre-transfer region of the toner image bearing member. The heat transfer station provides selective cooling and heating of the toner image bearing member.
A preferred printing apparatus employing a heat transfer station in accordance with the invention has a toner image forming station, an intermediate transfer member and a transfuse member. The toner image from the toner image forming station is transferred to the intermediate transfer member at a first transfer nip. The toner image is then transferred from the intermediate transfer member to the transfuse member at a second transfer nip. At a third transfer nip the toner image is transferred from the transfuse member, and generally simultaneously fused, to a substrate to form a document. The transfer from the intermediate transfer member, to the transfuse member is preferably rheologically assisted. The rheological assist is created by maintaining a preestablished temperature differential between the intermediate transfer member and the transfuse member. The transfer can further be electrostatically assisted. Therefor the intermediate transfer member is heated prior to the second transfer nip to heat the toner image supported on the intermediate transfer member.
However, the toner image forming station can be susceptible to excess heat, particularly when the toner image forming station employs a photoreceptor. As a result, a relatively elevated temperature in the first transfer nip can damage the toner image forming station resulting in decreased image quality. In view of the preference to heat the toner image prior to the second transfer nip, and to prevent excessive heat from damaging the toner image forming station, heat on the intermediate transfer member is transferred from the region of the intermediate transfer member intermediate the second and first transfer nips in the process direction to the region of the intermediate transfer member intermediate the first and second transfer nips in the process direction. In other words, the heat transfer station transfers heat from the post-second transfer nip region of the intermediate transfer member to the pre-second transfer nip region of the intermediate transfer member.